In a process of manufacturing a seamless can, printing is carried out on a can body after forming a can main body in which, the can body and bottom are integrated. In a curved surface printing machine which is used for printing on the seamless can, the can main body which is subjected to printing is externally fitted on a substantially circular cylindrical mandrel, and the printing is carried out in a state of being supported by a cantilever. The printing on the can body is to be carried out by relief printing or waterless offset printing.
In a case of carrying out curved surface printing on the can body by offset printing for instance, ink which has been held on a blanket is transferred onto the can body by moving the blanket by rotating a blanket wheel around a central axis thereof, while pressing an outer peripheral surface of the can body against an upper surface of the blanket. Consequently, the ink is printed in a circumferential direction of the circular cylindrical shaped can body.
For printing on the can body, the ink is to be transferred onto a can body 260 such that an overlapping portion 240 is formed as shown in FIG. 8. Here, FIG. 8 is a cross-sectional view in a direction of thickness, showing ink layers in the overlapping portion 240 on the conventional can body 260, and in a periphery of the overlapping portion 240.
The overlapping portion 240 is formed by transferring the ink onto the can body 260 by overlapping of ink layers corresponding to a front-end portion 210 in a circumferential direction of a printing direction, and a rear-end portion 230 in the circumferential direction respectively, or in other words, a printing-start portion and a printing-end portion of a printing plate, out of an ink layer 200 which has been transferred onto the can body 260.
A varnish 250 is applied by a varnish applicator on the ink layer 200 which has been transferred, and thereafter, the ink layer 200 with the varnish 250 applied thereon is dried by heating in an oven.
After the varnish 250 and the ink in the ink layer 200 are dried, the can main body is subjected to a neck-in processing, and upon being subjected to a flanging processing, the can becomes a seamless can.
As a method for the neck-in processing, currently, a die-neck processing in which a die is used, or a roll-neck processing in which a roll is used, is available.
A neck portion is formed to have a single-stage or a multi-stage shape, or a smooth shape. After the seamless can is filled with a content, a lid which is manufactured separately is double-seamed, and a sterilization process at a high temperature is carried out in a pasteurizer or a retort apparatus, depending on the content.
Patent Literature 1: Japanese Patent Application Laid-open Publication No. 2002-103775